Core for electric induction coils



Patented June 14, 1932 UNITED STATES PATENT OFFICE LESLIE GIDDENSBBAZIER AN D JAMES URMSTON, 01 LONDON, ENGLAND CORE FOB ELECTRICINDUCTION COILS No Drawing. Application filed August 28, 1929, Seriallo.389,096, and in Great Britain September 14,- 1928.

This invention relates to the manufacture of iron cores of electricinduction coils, particularly to those coils used in connection withlong distance telephony and known as loading I coils.

It is well known that a suitable core can be made by compressing ironpowder into a coherent mass, in a suitable mould. Inorder that such acore shall have the required elec- 10 tro-magnetic characteristics, ithas been found necessary that the individual grains of iron shall bemagnetically separated and preferably also electrically insulated fromone another, at the same time the iron grains 15 must be packed asclosely to one another as possible. I

It is the object of this invention to produce such cores by the use ofan insulating material which is better suited to the requirements of 10the case than the materials now in use.

The material used for producing the nec essary insulation of the irongrains is one possessing the following properties. It must be in a stateof extremely fine subdivision, each individual particle must be capableof resisting shear under pressure, and the material must be areasonably'good magnetic and electrical insulator.

A .material which .embodies these three properties in a highly efiectivedegree is a treated form of china clay, known as osmotic kaolin, whichis in a state of extremely fine v division. This kaolin is produced bycataphoresis in what is known as the osmotic process and is particularlysuitable on account of its extreme purity and fine division.

Kaolin, as it occurs in nature, isa clay consisting of a mixture ofparticles differing considerably in size. A proportion of these are ofcolloidal dimensions and a proportion are of materially largerdimension. By cataphoresis it is possible to remove the smallerparticles from a suspension in water and separate them from the largerparticles. It is with the particles of colloidal, dimensions soseparated that the present invention deals. Such particles are takenwithout mixture with water and are distributed throughout a mass ofgrains of magnetic material and with 10 or without a binder,'such asshellac, and the whole is consolidated under pressure without employinga temperature approaching the fusion points of the kaolin. By this meansthe kaolin is in its original form in the final product,.that is to say,the particles retain their natural toughness which peculiarly fits themfor the function of separating the magnetic grains during and afterconsolidation by high pressure. By this means it is ensured that,although the grains of magnetic material are forced very close together,they are still separated by spaces of very small dimensions in which thesmall particles of kaolin are situated.

The invention accordingly consists in using, as the-insulating materialin a core of the kind indicated, kaolin in a state of subdivision inwhich the particles are of colloidal dimensions, of which osmotic kaolinis an example. The cores are manufactured without the use of hightemperatures such as those at which partial or incipient fusion of thekaolin may take place with the aid of a flux.

It has been found that a suitable mixture can be formed containing up to10% by weight of the treated kaolin, depending to a great extent uponthe division of the iron.

The mixing may be carried out in any convenient manner. If the kaolin isthoroughly dried, it can be mixed dry with the iron powder by mechanicalagitation, or another method is to suspend the kaolin in an easilyevap-- orated liquid, such as alcohol, mix the suspension thoroughlywith the powdered .iron and then evaporate off the alcohol.

In order to facilitate the coherence of the mass under pressure a smallquantity of shellac or," similar material may be introduced into themixture, either by dry mixing or by evaporation from solution or by anyother known means. This shellac merely fills up the interstices betweenthe grains of iron and kaolin and tends to bind the mass together. It isnot relied on in any way for either the ma etic or electrical insulationof the grains 0 iron.

The grains of the kaolin whilst having theproperties of both magneticand electrical insulation are extremely small, and enable the irongrains to be packed closer together than hitherto, whilst stillretaining the necessary insulation from one another. Furthermore thekaolin does not become liquid or 5 lose its propert of resistin shear,which enables extreme y high mou ding pressures to be used without riskof bringing the iron grains in contact one with another.

What we claim as our invention and de 10 sire to secure by LettersPatent is A core for anelectric induction coil com prising powderedmagnetic material and in-. sulating material for separating the magneticgrains, mixed together and consolidated by 15 high pressure, in whichthe insulating material is unfused osmotic kaolin.

In testimony whereof we aflix our signatures.

LESLIE GIDDENS BRAZIER. 2 JAMES URMSTON;

